Defibrillator with controllable discharge switch

Abstract

Defibrillation of a heart ensues using a charging capacitor connected via a controllable switch arrangement to electrodes arranged in the region of the heart, the switch arrangement being operated to discharge across the heart tissue. In order to limit the initial current to a value not significantly exceeding the minimum value necessary to effect defibrillation, the controllable switch arrangement includes two contacts between which a contact maker, for example a mercury drop, is disposed, which is deformable under the influence of an electro-mechanical transducer. The transducer is arranged such that the contact maker connects the two contacts to one another given a prescribed excursion of the electro-mechanical transducer and, given a change of the excursion departing from the prescribed excursion, varies the electrical resistance between the contacts. The drive of the controllable switch arrangement ensues with turn-on pulses having a pulse height that is variable for setting the desired electrical resistance between the contacts.

We claim as our invention: 
     
       1. A defibrillator comprising: a capacitor;   means for charging said capacitor with energy;   electrode means for delivering said energy from said capacitor to a heart for defibrillating said heart;   controllable switch means connected between said capacitor and said electrode means for selectively controlling said delivery of energy to said heart, including two normally-open electrical contacts, a contact maker disposed between said two contacts, said contact maker consisting of deformable material having a restorative force which normally maintains said contacts open, electro-mechanical transducer means disposed for acting on said contact maker given a predetermined excursion of said transducer means, for deforming said contact maker to make an electrical connection between said two contacts, and given an excursion deviating from said predetermined excursion, for varying the electrical resistance of said connection between said two contacts; and   control pulse generator means connected to said electro-mechanical transducer means for supplying a control pulse thereto having a variable pulse height for selecting said electrical resistance between said two contacts.   
     
     
       2. A defibrillator as claimed in claim 1 wherein said control pulse has a pulse duration, and wherein said control pulse generator means includes means for varying said pulse height of said control pulse for reducing said electrical resistance between said two contacts over said pulse duration. 
     
     
       3. A defibrillator as claimed in claim 1 wherein said contact maker is deformable to cover areas of different size of said two contacts dependent on said excursion of said electro-mechanical transducer. 
     
     
       4. A defibrillator as claimed in claim 3 wherein said contacts consist of a resistor material. 
     
     
       5. A defibrillator as claimed in claim 1 wherein said contact maker is deformable to cover different regions of said contacts dependent on said excursion of said electro-mechanical transducer. 
     
     
       6. A defibrillator as claimed in claim 5 wherein said contacts consist of a resistor material. 
     
     
       7. A defibrillator as claimed in claim 1 wherein said contact maker consists of a predetermined quantity of a conductive liquid. 
     
     
       8. A defibrillator as claimed in claim 1 wherein said electro-mechanical transducer means comprises a drive element selected from the group consisting of piezoelectric, electro-magnetic, magnetostrictive and electrostrictive drive elements. 
     
     
       9. A defibrillator comprising: a capacitor;   means for charging said capacitor with energy;   electrode means for delivering said energy from said capacitor to a heart for defibrillating said heart;   controllable switch means connected between said capacitor and said electrode means for selectively controlling said delivery of energy to said heart, including a first contact consisting of material capable of electrical conduction, a second electrode having electrically insulating regions and regions capable of electrically conducting, said first and second contacts defining a chamber therebetween, a contact maker disposed in said chamber consisting of deformable material having a restorative force which normally maintains said contact maker in an electrically insulating region of said second contact, electro-mechanical transducer means attached to one of said contacts for acting on said contact maker to deform said contact maker and bring said contact maker into contact with a region of said second contact which is capable of electrically conducting to make an electrical connection between said first and second contacts given a predetermined excursion of said transducer means, and for deforming said contact maker given an excursion deviating from said predetermined excursion for varying the electrical resistance of connection between said two contacts; and   control pulse generator means connected to said electro-mechanical transducer means for supplying a control pulse thereto having a variable pulse height for selecting said electrical resistance between said two contacts.   
     
     
       10. A defibrillator as claimed in claim 9 wherein said second contact comprises a plate consisting of resistor material having a plurality of annular regions therein consisting of insulating material. 
     
     
       11. A defibrillator as claimed in claim 9 wherein said first contact consists of resistor material.